Phase Shift Keying
PSK Op Amp
This is the simulator in full action: http://everycircuit.com/circuit/6303581695901696
Op Amp mainly wants both of its input to be equal votlage and will do this through a feedback loop from output to one of the inputs.
Op Amp will be the same as the AC source untill the non inverting input (+) is shorted to ground by the mosfet.
When shorted, the Op Amp output will go in reverse of the AC source.
Look at the bottom and top middle Op Amp and see how this apply.
And this is a link to Schmitt Trigger (Op Amp on top right)
http://www.circuitstoday.com/schmitt-trigger-using-op-amp
